The present invention relates to a an image transfer system for the high speed conversion of digital image data to film and for reading film to produce digital image information.
The desire for better resolution for television, video production, broadcasting, motion picture production and other uses has led to the development of high speed scanners. For the present purposes the term scanner will be used to designate an optomechanical system that deflects light and/or moves media to produce motion of a focussed spot or line for the purpose of reading or writing information from/to the media. In this context a scanner designates both a reader which recovers data in digital form from previously recorded media and a recorder which exposes media in accordance with digital data. Early scanners used cathode ray tubes in combination with deflectors. The latter scanners include continuous motion systems which scan line by line and suffer from jitter and weave of the film and stationary systems which customarily used a pin-registered gate to hold the film accurately relative to the perforations. Line scan systems generally operate in real time at a rate of 25 frames per second. Such devices employing electron beams suffer from poor geometric accuracy, a lack of resolution, a lack of uniformity and low optical power which limits both the reading and recording speed. A major reason for the inaccuracy, lack of uniformity and poor resolution is due to the tube electron beam deflection systems and optics required to image the tube face onto the film. The CRT spot size and end use format requirements imposed by broadcast TV requirements result in a limited resolution for such devices.
Scanners have also employed laser rather than CRT beams. Laser telecine machines which convert film to video image data in real time and scan the film line by line have been developed for high definition television. High definition television employs twice as many scan lines as conventional television and hence provides greater resolution- More recent laser systems have achieved high speed but involve relatively complex optics which affect the quality of the imaging. Moreover, the latter systems are not useful when the final format is film for general theatrical release or where the user desires to retain the original film quality for archive, or reformatting purposes. For the latter situations a high resolution over a large area at a reasonably high speed is required.
Accordingly, it is an object of the present invention to provide an improved image transfer system. It is a further object of the invention to provide a high speed film scanner capable of a large scan angle and a small scanning spot. Yet another object is to provide a scanner which is capable of providing high resolution and geometric accuracy independent of image size.